1. Field of the Invention
The present invention relates to an optical device package and an optical semiconductor device using the same, and more particularly to an optical device package to mount an optical device used especially in electronic information devices and information communication devices to transmit and receive high frequency signals, and an optical semiconductor device using the same.
2. Description of the Related Art
In recent years, as broadband optical communications and public telecommunication networks using optical fibers have become widely used, there has been an increasing need to transmit a large amount of information at low cost. This means that electronic information devices for such communications and networks must handle a huge amount of information. That is, these electronic information devices must be reliable and low in cost, yet capable of processing a large amount of data at high speed.
Semiconductor laser devices, which are a major component of electronic information devices, are also required to be low in cost and capable of efficiently generating an oscillation at high power.
Further, recent years have seen an increasing need for DVD-R/RW drives, which are one of the high speed, high capacity storage devices. DVD-R/RW drives employ a high power semiconductor laser, and efforts have been made to develop a high efficiency, high power semiconductor laser formed of an AlGaInP/GaAs material in order to process information at high speed. An optical semiconductor device employing such a semiconductor laser must be adapted to meet requirements such as stable performance at high power operation, low cost, and high efficiency.
The semiconductor laser used in an optical semiconductor device is mounted in a can package having a coaxial configuration (a low-cost configuration) to provide reduced cost. Even such a can package must have a configuration that allows for easy mounting and provides good heat dissipation characteristics, stable optical characteristics, and reduced high frequency signal transmission loss during operation.
The main body of the can package is referred to as the “stem,” and includes: a metal disc called an “eyelet”; a plurality of rod-shaped lead electrodes for carrying electrical signals disposed to extend through a plurality of through-holes formed in the eyelet, or metal disc (the through-holes being hermetically sealed with a seal glass); and a mount called a “block” disposed on a disc surface of the eyelet, or metal disc, and configured to have an optical device bonded thereto.
Plastic or resin molded semiconductor laser devices employing such a can package have been proposed which provide reduced manufacturing cost and increased freedom in designing their shape.
A first known plastic molded semiconductor laser device (an example of a plastic molded package) includes arc-shaped portions internally tangent to a virtual circle centered at the point of light emission of the laser diode (or LD) chip. This semiconductor laser device can be fitted and fixed into the stepped receiving hole of a device in the same manner as can-type semiconductor laser devices. (See, e.g., paragraphs [0021] and [0022] and FIG. 2 of Japanese Laid-Open Patent Publication No. 7-335980.)
A second known plastic molded semiconductor laser device is constructed such that: the laser element is mounted on a lead frame perpendicularly protruding from the center portion of a flat surface of the cylindrical plastic base; and the side portions of the lead frame are reinforced with their respective resin members molded thereon, each resin member having a vertically symmetrical shape. This configuration provides increased design freedom, reduced cost, reduced thermal deformation, and hence a reduced amount of shift of the point of light emission during laser operation. (See, e.g., paragraphs [0010], [0021], and [0035] and FIG. 1 of Japanese Patent Publication No. 3607220.)
A third known plastic molded semiconductor laser device includes: a metal eyelet member including an eyelet base portion having a semicircular shape as viewed in plan and an element mounting portion integrally formed with the eyelet base portion, wherein the element mounting portion protrudes from the eyelet base portion; and a lead pin unit including two (signal) lead pins and one ground lead pin and plastic molded components such as projections, a flat plate portion, and a lead support portion, wherein the projections are engaged in the eyelet member, wherein the flat plate portion is joined to an inner edge surface of the eyelet base portion, and wherein the lead support portion supports and holds the lead pins in place. The eyelet member and the lead pin unit are separately manufactured and then assembled together. This configuration enhances heat dissipation from the eyelet member, allowing for accommodation of a high power LD and accurate alignment of the optical axis. Further, since the lead pin unit is molded of a resin and the (signal) lead pins and the ground lead pin in the lead pin unit are supported by the lead support portion, these lead pins can be prevented from bending during transportation of the lead pin unit. (See, e.g., paragraphs [0010], [0014], and [0027] and FIG. 1 of Japanese Laid-Open Patent Publication No. 2004-311707.)
However, each of the above configurations has disadvantages. In the case of the first known plastic molded semiconductor laser device, the above-described arc-shaped portions (which constitute protrusions protruding from the die pad portion) may be difficult to reliably form to a desired shape, although they are compatible with conventional can packages. That is, this configuration only provides for an improved lead frame.
In the case of the second known plastic molded semiconductor laser device, the resin base (corresponding to the eyelet of a conventional can package) is formed by a simple resin molding process, which is advantageous. However, a resin mold (or resin eyelet) has lower thermal conductivity than a metal eyelet. Therefore, this semiconductor laser device may exhibit degraded heat dissipation characteristics and, furthermore, degraded optical characteristics due to the shift of the point of light emission caused by thermal deformation at high temperatures if it employs a high power LD, which has become widely used in recent years.
In the case of the third known plastic molded semiconductor laser device, the (signal) lead pins and the ground lead pin are supported by the lead support portion molded of a resin. Therefore, most of the entire lengths of these (signal) lead pins and ground lead pin is covered and sealed with the resin lead support portion; only their tip portions are exposed. This configuration results in an increased distance between the LD chip and the grounding layer on the surface of the resin substrate (on which the LD chip is mounted), leading to increased inductance and hence increased transmission loss at high frequencies. This adversely affects the laser output characteristics, which may make it difficult for the semiconductor laser device to achieve good high frequency characteristics.